1. Field of the Invention
The present invention relates to electric conductive and sliding resin material. More particularly, the present invention relates to resin material to which both sliding characteristics and electric conductivity are imparted so that the material can be used as a cassette reel of a VTR, a rotary member for paper feeding in a copy machine, and parts of other business and electronic machines.
2. Description of the Prior Art
Recently, demands for VTRs have been rapidly increasing, and the employment of antistatic resin as cassette reels has greatly contributed to the spreading of and quality enhancement of VTRs since it prevents the occurrence of electric discharge in the cassette reels during the running period of a tape, in which period static electricity is liable to be generated due to friction between the tape and the cassette reels or due to the peeling off of the tape, thereby exerting an adverse effect on the appearance of the VTR. In addition, during the rotation of a reel plate which is integrally rotated with a pulley driven by a belt, the reel plate is electrically charged due to friction between the belt and the pulley and then the electric charge is discharged into the ICs of the VTR via the reel plate, with the result that failure of the VTR occasionally occurs. This failure can be prevented by the employment of antistatic resin.
Furthermore, in electrostatic-type copy machines, the plastics presently used for bearing or supporting paper-feeding rollers can be charged by the static electricity of the charged paper, with the result that such problems as copy unevenness, inaccurate paper feeding due to the adhesion of paper to the paper-feeding roller, and discharge of an electric charge from the paper-feeding roller can arise. These problems can be solved by providing a copy machine with an antistatic means or a mechanism for peeling off paper adhered on the paper-feeding roller. However, when this is done, since a copy machine mechanism and means are complicated, the reliability of the copy machine is lessened and the weight and cost thereof are increased.
Macromolecular materials, such as plastics, usually have a volume resistivity of 10.sup.14 .OMEGA..multidot.cm or more. Thus, an electric charging phenomenon is very liable to be generated in macromolecular materials due to friction or the like. When an electric charging phenomenon is generated, dust is adsorbed on the macromolecular materials or an electric impact is imparted to the macromolecular materials. An antistatic agent is therefore blended with the macromolecular materials when a measure against dust adsorption is necessary.
Commercially available antistatic macromolecular materials are not satisfactory for use as the reel plate of a VTR since, in order to improve the appearance, not only do the components need to be antistatic but they also need to be highly electric conductive so that the electric charge is shunted to the ground.
In order to provide plastic materials which have a high resistance against electromagnetic interference, as in the case of plastic materials used as housings of electronic devices such as microcomputers and VTRs, an electric conductivity needs to be imparted thereto.
Known methods for imparting electric conductivity to macromolecular materials, such as plastics, are: (1) the incorporation of conductive carbon particles thereinto, (2) the incorporation of metal powder or metal fiber thereinto, (3) the incorporation of carbon fiber thereinto, and (4) the metallization thereof.
The metallization method (4) can be used for the housings of electronic devices and for ICs but cannot be used for sliding members, such as bearings, rollers, and the like. If the metal-fiber or metal-powder incorporating method (2) and the carbon-fiber incorporating method (3) are employed in the production of the sliding members to enhance their electric conductivity, flaws may disadvantageously be formed on their opposite members. In addition, when the sliding members, into which carbon fibers are incorporated, are subjected to friction over a long period of time, their coefficient of friction disadvantageously increases.
Method (1) is described in U.S. Pat. Nos. 3,823,217, 3,243,753, 3,823,217, and 3,861,029.
In method (1), carbon blacks are used as conductive carbon particles since the volume resistivity of the carbon blacks is lower than that of other carbonaceous materials. Although the electric conductivity is enhanced by the carbon blacks, the sliding characteristics are so impaired as compared with macromolecular materials free of carbon blacks that macromolecular materials containing carbon blacks cannot be used as bearings.
Sliding resin materials containing graphite powder are known from, for example, U.S. Pat. No. 4,302,379 and GBP No, 1,069,919.
GBP No. 1,044,028 discloses a sliding resin material containing metal oxide, carbon black, or silica as an inert filler.